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Fluid Control - solenoids valves & pumps - little ones? — Parallax Forums

Fluid Control - solenoids valves & pumps - little ones?

David HalsellDavid Halsell Posts: 2
edited 2006-03-01 11:16 in General Discussion
Hi All,

I need to control very small quantities of water very precisely with a BS2. (for example, a single drip at specified intervals)

Does anyone know where I can get low pressure, micro solenoids valves & pumps without breaking the bank? Everything I have found is either too big or too spendy.

thanks!
David

Comments

  • SteveWSteveW Posts: 246
    edited 2006-01-27 16:23
    How about (ab)using a Parallax / HP Inkjet cartridge? Precise, low-volume liquid metering is sort of their job description...

    Steve
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-27 17:08
    You may be able to easily create your own by using a Servo Motor as your shut-off.

    Since you say low pressure and low volume, I presume that you may be using plastic tubing that is quite flexible.
    Rather than inserting a valve, you can simply 'pinch' the tubing between a backing and an eccentric cam [noparse][[/noparse]provided by the servo].

    If you look at small pulleys and drive spools for rubber belted motors, you can use these to secure your tubing into a good configuration.

    This has the added advantage of you already having BS2 code for the SERVO which is quite predictable in terms of both movement and speed.

    Medical units use something similar to pump blood in their Heart and Dialysis Machines as it is all quite serile and avoids leakage. That is a bit more complex, but gives a good example of how to pinch your tubing.· You can also create a very good pump with a similar setup.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 1/28/2006 9:26:40 AM GMT
  • Eric REric R Posts: 225
    edited 2006-01-28 02:33
    Kramer said...
    You may be able to easily create your own by using a Servo Motor as your shut-off.

    Since you say low pressure and low volume, I presume that you may be using plastic tubing that is quite flexible.
    Rather than inserting a valve, you can simply 'pinch' the tubing between a backing and an eccentric cam [noparse][[/noparse]provided by the servo].

    If you look at small pulleys and drive spools for rubber belted motors, you can use these to secure your tubing into a good configuration.

    This has the added advantage of you already having BS2 code for the SERVO which is quite predictable in terms of both movement and speed.

    Medical units use something similar to pump blood in their Heart and Dialysis Machines as it is all quite serile and avoids leakage. That is a bit more complex, but gives a good example of how to pinch your tubing.

    I agree with the above post. This would have to be the cheapest route.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-28 17:15
    Ok you can call me god (just kidding), I have just the ticket for you. My ex works in home health care. While we were dating she brought home something called a kangaroo pump. It is a IV pump for at home patients, I diasected the thing and extracted an SLA brick, a very nice 12 charactor display board (using 3 HDLG-2416s) and a keypad, all of which I have used in subsequent projects. The piece I kept that I haven't used is the mechanical harware for controlling the flow of the IV fluid, you place a certain diameter tubing in the front that sandwiches in·the front panel, it comes in contact with this cam which moves these bars in a wave-like fashion, moving the fluid in a very consistant manner (the thing had to measure ml/hr), the cam is driven by a cog pulley and belt system which is driven by a gearboxed motor. The only problem with the system is that the electrical tabs to the motor have been ripped off (ex did this before I pushed her aside and said "let me do it" (she was only interested in the mechanical assembly, but then changed her mind about keeping it)). You may be able to pry the plastic back to the motor to get at the tabs inside the motor, or find another gearbox motor with a shaft compatible with the diameter and set screw for the cog. I'll send it to you for the cost of shipping, contact me via PM if you are interested and we can exchange addresses. Enclosed are some pictures of it, the camera wanted to focus on the pattern in the couch so they are a little fuzzy, but it should give you a good idea of what the unit looks like.

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  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-28 17:23
    Oh, just reread the original post (read it a couple of days ago, forgot the micro-size requirement when I had the lightbulb go off today), sigh I fear the unit will be too big for your requirements. The unit is 5" across, 4" high, and 3.5" deep, Id say the entire thing weights 1-2 lbs. But you can still have it if you think it will fit your needs. Oh also it was designed that the feeder fluid is gravity fed.

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-01-29 10:03
    The 'Kangaroo Pump' is quite interesting and useful.

    This or similar devices are used to deliver morphine to terminally ill cancer patients. While that may seem quite morbid, the point is that they are well calibrated and quite programable.

    All you have to do is lay the tube through the device and you have adapted a normal IV tube from gravity drip to pump.

    {I am not fixated on drug devices, m Dad was an M.D.}

    The fact is this brings to mind a whole area of robotic resources that are sitting in junk piles and storage rooms of hospitals.
    There is the obvious wheel chair, but also tons of carts.· An IV stand, with wheels can suspend a power cord.· Generally everything is heavy duty and often stainless steel.

    The only problem is how and where to get a hold of 2nd hand stuff.· From what I understand, much of it is exported to the needy in oversea's locations as a 'non-profit' can easily sell items to the general public or 'for profit' ventures [noparse][[/noparse]it is all in the IRS tax code about non-profit organizations].

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 1/29/2006 10:16:50 AM GMT
  • ktekxktekx Posts: 71
    edited 2006-01-29 11:42
    Working off the servo idea, you might want to try chemistry burets. They allow for pretty precise control "dripping" by controlling a knob. They work strictly with gravity and depending on how much liquid you are planning to hold, it may not be small enough, but just thought I'd pitch an idea.
  • Lee HarkerLee Harker Posts: 104
    edited 2006-01-30 14:35
    David,
    We use a soldering station that uses syringes of solder paste and flux. The syringes have various size tips for different "blob" sizes. They are not like medical syringe tips with a sharp point. I have seen syringe applicators that are driven by a stepper motor and some that are pushed with compressed air attached where the plunger would be. In the case of the flux and solder paste, the size of the droplet is determined by the syringe tip size and the duration of the air pressure applied.

    Lee Harker
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-30 17:02
    Pneumatic dispensing stations are expensive though (starting in the low-mid hundreds for the units Ive looked at). Ive sent him the kangaroo pump assembly (hard to beat a <$5 price (shipping)), and he's going to investigate if it will work for what he needs.

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  • David HalsellDavid Halsell Posts: 2
    edited 2006-01-30 17:25
    Thanks for the great ideas, I appreciate all your input!

    David
  • datsun2literdatsun2liter Posts: 5
    edited 2006-03-01 02:14
    When I was working in a lab in grad school we had these cool little pumps, the use a rotating head that has rollers around it.
    You stretch rubber tubing around the rotating head. The pressure of the rollers keep fluid from escaping by gravity.
    They are very accurate.
    You could probably get more information by looking at pumps in some of the scientific supply houses, Sargent Welch for example,
    find something that might work, then hit the manufacturers web site for photos.,,

    Pharmacia makes chromatography equip, very nice, very expensive, i think they sell such a pump (They're Swedish, so their stuff is like a Volvo)

    A stepper motor driving one of these heads would do the trick...

    I can draw it and email it too you or post it, if you like..

    Finally think about ebay, they sell alot used scientific equip..

    Kangaroo pumps are really not that accurate, if they really want accuracy now we use syringe driven delivery systems...

    all the patient controlled anesthesia, PCA, is syringe driven...
  • steve_bsteve_b Posts: 1,563
    edited 2006-03-01 02:59
    the same type of pump/roller device you describe is in commercial dishwashers. They dispense the soap and degreaser in to the machine via cam settings.

    Might want to keep an eye out for old kitchen gear getting tossed!

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    ·

    Steve

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • SteveWSteveW Posts: 246
    edited 2006-03-01 11:16
    Yep - peristaltic pumps. Relatively cheap on ebay.

    http://search.ebay.co.uk/peristaltic

    Steve
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